Method for determining when a communication device should rate shift or roam in a wireless environment

ABSTRACT

Methods for improving communication performance in a wireless communication system where the wireless communication system has at least one mobile wireless communication device and a plurality of transmitter/receiver sites. The transmitter/receiver sites have a geographic area, defined as a cell, within which the mobile wireless communication devices can communicate with at least one of the transmitter/receiver sites. The methods determine when the mobile wireless communication device should rate shift or roam based on connection quality measurement data or position information such as GPS. In one method, the measurement data is subjected to configurable parameters to create a functional relationship value that is recorded. The recorded functional relationship values are trended and extrapolated to determine whether a rate shift or roam should be performed. In a second method, the measurement data taken prior to a communication connection failure is stored in at least one data vector with there being at least one data vector for each rate shift and one for roam. A functional relationship utilizing current measurements, last data rate, and the respective data vectors determines whether a rate shift or roam should be performed. In a third method, the position information for the wireless communication device is compared to at least one transmitter/receiver site and a determination is made as to the optimal transmitter/receiver site for communication.

CROSS-REFERENCE TO RELATED APPLICATIONS Claiming Benefit Under 35 U.S.C.

This application is a continuation of application Ser. No. 09/342,315,filed Jun. 29, 1999 now U.S. Pat. No. 6,791,959, which is acontinuation-in-part of application Ser. No. 09/291,581, filed Apr. 12,1999, which issued as U.S. Pat. No. 6,556,553 on Apr. 29, 2003. Each ofthe aforementioned cases are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication systems, andmore particularly, to a method for determining when a wirelesscommunication device should rate shift or roam in order to improvecommunication performance.

2. Description of Related Art

The ability to communicate with people on the move has evolvedconsiderably since Guglielmo Marconi in 1897 first demonstrated radio'sability to provide continuous contact with ships sailing the EnglishChannel. Since then new wireless communications methods, includingmobile radio communications, have grown by orders of magnitude, fueledby electronic miniaturization technologies and the large-scaledeployment of affordable, easy-to-use, radio communication networks.

Examples of a radio communication network are a wireless local areanetwork (WLAN) and a wireless wide area network (WWAN). A WLAN comprisesa plurality of wireless communication devices that communicate usingradio frequency (RF) signals. As in a wired local area network (LAN),the WLAN allows users to seamlessly access disk drives, printers, andadditional computer resources and systems connected to the WLAN. Thewireless communication devices include a radio receiver/transmitteradapted for RF communication with the other elements of the WLAN. TheWLAN may also include a central host processing unit that sendsinformation to and receives information from any one of the plurality ofremotely disposed communication devices. The WWAN expands upon thefeatures of the WLAN and offers extended geographic coverage for thecommunication network that may include a state or even countries.

The central host processor may also form part of a separate wired LAN toprovide a bridge with the WLAN. In such a WLAN, the wirelesscommunication devices may comprise portable units that operate within adefined environment to report information back to the central hostprocessing unit. In general, the defined wireless environment may befurther divided into basic service areas or cells that are supported bytransmitter/receivers of the WLAN for providing segmented but completewireless coverage for the wireless communication devices over thedefined area. The WWAN may incorporate these features of the WLAN or maybe a completely-wireless network. Thus, WLAN and WWAN systems offerincreased flexibility over wired LAN systems by enabling operators ofthe wireless communication devices substantial freedom of movementthrough the environment, and are particularly useful for remotecommunication and data collection applications such as inventorycontrol, manufacturing and production flow management, and assettracking.

For example, in a WLAN or WWAN, a mobile worker may move throughout thework area carrying a wireless communication device such as a portableterminal or computer. The work area may be within a building or from onebuilding to another and the mobile worker may move from one cell toanother. The wireless device must maintain a wireless connection that istransparently maintained so that the central host processing unit andthe mobile worker can perform their assigned tasks. As the workertravels within a cell or from one cell to another, it may becomenecessary for the wireless communication device to lower thetransmission rate in order to maintain the connection to thetransmitter/receiver of the current cell. Alternatively, the wirelesscommunication device may switch (also known as roam) from the currentcell to another cell that may offer better connection quality to thecommunication network. In either case, the wireless communication devicemust make this transition without a loss of connection or servicedegradation being noticed by the mobile worker or the central hostprocessing unit. The transition should be seamless and appear andoperate as a wired connection.

In a typical WLAN or WWAN, the wireless communication device determineswhether to rate shift or roam based on (1) the failure to successfullytransmit and/or (2) comparison of the connection quality between one ormore cells with respect to (i) an acceptable predefined threshold or(ii) connection quality. These methods for rate shifting or roaming arerelatively inflexible. For example, they cannot be easily modifiedthrough configuration parameters or dynamically based on the wirelessenvironment. Furthermore, these methods also react to the state of thewireless connection rather than anticipate the state. By reacting to thestate of a connection, the decision to rate shift or roam occurs at themoment when the wireless communication device is ready to transmit. Thisresults in slower response times as conditions change. The wirelessnetwork performance suffers and utilization difficulties arise such asdelays in transmission, necessary retransmissions, loss of data, orunintelligible voice connections. Finally, there may be a completeconnection loss between the wireless communication device and thecentral host processing unit.

Under some current implementations, delays in rate shifting and/orroaming within a cell or to a new cell may result in the loss of data,voice, or a network connection, such as a TCP/IP network connection,between the wireless communication device and the central hostprocessing unit. When a data or network connection is lost, the workermust reinitiate a logon sequence to the host, then to the requiredapplication, and finally repeat the work that was lost. Similarly, whena voice connection is lost, the worker must reestablish the connection,determine at what point in the conversation did the connection fail, andthen repeat the conversation for at least the portion that was lost. Ifthe mobile worker is in a location situated at a cell boundary or at theboundary of several cells, the wireless communication device may beunable to effectively maintain a connection due to interference ormarginal signal quality. The worker then would be unable to perform theassigned tasks because of the communication connection failure.

This situation can be further aggravated by changing conditions within acell or among cells of the wireless environment. For example, inventorymoved around within a warehouse or workspaces that are reconfigured canaffect communication performance, including cell coverage, and placeincreased demands upon the rate shift and roam functions.

Accordingly, it would be desirable to provide a method for determiningwhen a communication device should rate shift or roam in a wirelessenvironment. The method would improve communication connections andperformance by reducing the number of required retransmissions, offer anoptimum bandwidth, and faster response time. The method would furtherreduce network connection losses due to the use of industry standardnetwork protocols by the wireless media. Furthermore, the method wouldbe flexible and anticipate the rate shift and roam requirements, even asthe communication environment evolves.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a method isprovided for determining when a communication device should rate shiftor roam in a wireless environment. The method improves communication bydynamically and flexibly anticipating when a rate shift or roam shouldoccur.

In an embodiment of the present invention, a method is provided forimproving communication performance in a wireless communication systemwhere the wireless communication system has at least one mobile wirelesscommunication device and a plurality of transmitter/receiver sites. Thetransmitter/receiver sites have a geographic area, defined as a cell,within which at least one mobile wireless communication device cancommunicate with at least one of the transmitter/receiver sites.

According to a first embodiment of the present invention, the methodcomprises obtaining at least one measurement related to a position ofthe wireless communication device and comparing the measurement relatedto the position relative to at least one of the transmitter/receiversites. A determination is made as to the optimal transmitter/receiversite to communicate with the wireless communication device. Themeasurements may comprise global position information, relative positionof the wireless communication device to the transmitter/receiver sites,and a proximity threshold for the transmitter/receiver sites. Thecomparing step may include measuring the relative position to theproximity threshold. The obtaining step may include obtaining datarelated to the transmitter/receiver sites for available channel,accessibility, and congestion level and this data may be used todetermine the optimal transmitter/receiver site. The method may includea further step of estimating the position of the wireless communicationdevice relative to the transmitter/receiver sites at a future point intime.

According to a second embodiment of the present invention, a storagemedium contains program instructions executable by a processor forimproving communication performance in a wireless communication system.The program comprises the steps for a method in accordance with thefirst embodiment described above.

According to a third embodiment of the present invention, the mobilewireless communication device, for the wireless communication systemdescribed above, has a memory and a processor that runs a program storedin the memory. The program comprises the steps for a method inaccordance with the first embodiment described above.

A more complete understanding of the method for determining when acommunication device should rate shift or roam in a wireless environmentwill be afforded to those skilled in the art, as well as a realizationof additional advantages and objects thereof, by a consideration of thefollowing detailed description of the preferred embodiment. Referencewill be made to the appended sheets of drawings that will first bedescribed briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram illustrating a communication system within afacility;

FIG. 2 is a system diagram illustrating a communication system thatincludes multiple facilities;

FIG. 3 is a flowchart diagram illustrating a predictive method fordetermining when a communication device should rate shift or roam in awireless environment in accordance with an embodiment of the presentinvention;

FIG. 4 is a flowchart diagram illustrating a heuristic method fordetermining when a communication device should rate shift or roam in awireless environment in accordance with an embodiment of the presentinvention; and

FIG. 5 is a flowchart diagram illustrating a GPS method for determiningwhen a communication device should rate shift or roam in a wirelessenvironment in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention satisfies the need for a method for determiningwhen a communication device should rate shift or roam in a wirelessenvironment that improves communications performance. The method wouldbe flexible, robust, and anticipate the rate shift and roamrequirements. Communication performance would improve due to the reducedretransmission requirements, faster response time, optimum bandwidth,and fewer connection dropouts. Network connection losses would besignificantly reduced and the method would dynamically adjust to theevolving wireless. communication environment. In the detaileddescription that follows, it should be appreciated that like referencenumerals are used to identify like elements illustrated in one or moreof the figures.

Referring first to FIG. 1, a communication system 10 is illustrated. Thecommunication system 10 includes a central host processor 12 connectedto a wired network 14. The central host processor 12 may, for example,consist of a UNIX based system that defines the host or applicationenvironment for the wired network 14. The wired network 14 media may,for example, consist of an Ethernet, Token Ring, or ATM, and utilizenetwork protocols such as TCP/IP, SPX/IPX, SNA LU6.2, as known in theart. The wired network 14 has a plurality of access points 16 that arecoupled to the wired network 14. The plurality of access points 16 aretransmitter/receivers that define basic wireless service areas calledcells 18 within which a wireless communication device 20 is in range tocommunicate with the respective access point 16 for the given cell 18.The radio frequency (RF) wireless links are represented symbolically byRF links 26. The access point 16 acts as a bridge from the wirelesscommunication arena defined by its cell 18 to the wired network 14.There may also be one or more wireless access points 22 that arewireless transmitter/receiver repeaters that define cells 24. Thewireless access points 22 can be used to extend the wireless coverage ofthe access points 16 and, in general, the communication system 10, byrelaying information to and from the wireless communication devices 20and the access points 16. There may also be multiple links from onewireless access point 22 to another until finally reaching the accesspoint 16.

FIG. 2 illustrates a communication system 30. The communication system30 expands upon the features of the communication system 10 of FIG. 1 byproviding wireless coverage not only within a building, but also amongseveral buildings or even within a city. The communication system 30includes a central antenna 32 that communicates through RF links 26 to aplurality of remote antennas 34. The central antenna 32 may be attachedto an administration building 33 or other central location based uponthe location of the remote antennas 34. The remote antennas 34 may belocated on various buildings 36 or other convenient remote locations.The building 36 may include a wired network 38 with a plurality ofaccess points 40. Each access point 40, as in FIG. 1, would consist of atransmitter/receiver defining a cell 18 that provides RF coverage forthe wireless communication devices 20. The access point 40 would providea bridge for the wireless communication devices 20 to the wired network38. There may also be wireless access points 42 that consist oftransmitter/receiver repeaters, as in FIG. 1. The wired network 38 isthen linked to the administration building 33 and its associated networkthrough the remote antenna 34 to the central antenna 32 and finallythrough its link to a wired network (not shown) within theadministration building 33.

In FIG. 1, as the mobile worker, with the wireless communication device20, moves throughout the work area, it is necessary to maintain thewireless connection between the wireless communication device 20 and thewired network 34 and ultimately to the central host processor 12. Thewireless communication device 20 may transition between one cell 18 toanother or between the cell 18 and the cell 24 covered by the wirelessaccess point 22. In FIG. 2, the wireless communication device 20 mayalso transition between buildings or comprise part of a wireless widearea network. The wireless communication device 20 may be within avehicle 44 that communicates through the remote antennas 34 or directlywith the central antenna 32, depending upon the communication system 30structure and the proximity of the vehicle 44 to the various cells ofthe system. Thus, the communication system utilized could be acompletely wireless network with the wireless communication device 20communicating through a number of antennas that are in communicationwith each other via wireless methods and provide coverage over a widegeographic area.

For the examples discussed above, the wireless communications canconsist of voice or data information, as known in the art. The wirelessconnection should be transparent to the mobile worker as the wirelesscommunication device 20 roams from cell to cell or rate shifts. Thereshould be no loss of connection or service degradation and it shouldappear as if there is a wired connection. If the RF connection begins todegrade, a determination should be made as to whether communicationperformance would improve by transmitting at a lower information rate orroaming to another cell offering a higher quality RF connection. Thisdetermination could be made by the wireless communication device 20having a processor and a memory, with the processor executing a storedprogram for carrying out the method steps discussed below.Alternatively, the method steps may be performed centrally, for example,by the network or a central host processor.

In accordance with a first embodiment of the present invention, apredictive method for determining when a communication device shouldrate shift or roam in a wireless environment is provided. FIG. 3illustrates the basic steps, in flowchart form, of the predictivemethod. The method would utilize various measurements to evaluateconnection quality, the measurement data obtained at step 50. Thesemeasurements may include but are not limited to: 1) signal-to-noiseratio (SNR); 2) bit error rate (BER); 3) number of transmission retries(NTR); 4) received signal strength indicator (RSSI); 5) bitenergy-to-noise density (E_(b)/N₀); 6) global position information(GPS); and 7) cell congestion information (also known as load factor).These measurements (m_(j)) would be utilized in conjunction withconfigurable parameters that controls the use of m_(j) such as: 1)utilization of a measurement (u_(j)) (e.g., yes/no); 2) how measurementis used (h_(j)) (e.g., weighting factor); and 3) related measurementdecision criteria (d_(j)) (e.g., threshold). At step 52, themeasurements, subjected to the configurable parameters, create afunctional relationship f_(j)(m_(j), u_(j), h_(j), d_(j)). Thefunctional relationship value is stored in memory at step 54. At step56, the value of function f_(j) in conjunction with measurements takenat prior time intervals t⁻¹, t⁻², . . . , t_(−n) with respective valuesof function f_(j−1), f_(j−2), . . . , f_(j−n) are trended andextrapolated to yield extrapolated value f_(j+1). The extrapolatedvalue, f_(j+1), is then used to determine, at step 58, whether to rateshift or roam prior to the next transmission.

Thus, this method evaluates the most recent measurements sampled andextrapolates future measurements based on the data trend. This allowsanticipation of the need to rate shift or roam rather than to wait foran unsuccessful transmission or comparison against a fixed predefinedthreshold. The prediction of future measurements can even be performedwhile the last transmission is taking place. Thus, a proactive approachfor rate shifting and roaming is adopted that can be critical when themobile worker is moving swiftly on a motorized vehicle or when usinghigh speed data and voice transmission rates.

In accordance with a second embodiment of the present invention, aheuristic method for determining when a communication device should rateshift or roam in a wireless environment is provided. This methodinitially only rate shifts or roams based on a failure to transmit orreceive. The values of measurement parameters that are being used tocharacterize the quality of a connection on every transmission orreception are recorded. When a failure occurs, the previous measurementstaken are stored in a data vector. There is one data vector for eachrate shift and one for roaming. The values in each data vector are thenutilized to establish the criteria to rate shift or roam.

FIG. 4 illustrates the basic steps, in flowchart form, of the heuristicmethod. This method would utilize various measurements, taken at step60, to evaluate connection quality. These measurements may include butare not limited to: 1) signal-to-noise ratio (SNR); 2) bit error rate(BER); 3) number of transmission retries (NTR); 4) received signalstrength indicator (RSSI); 5) bit energy-to-noise density (E_(b)/N₀); 6)global position information (GPS); and 7) cell congestion information.These measurements (m_(j)) would be utilized in conjunction withhistorical data vectors (r_(j)) that represent when a rate shift or roamshould occur. The historical data vectors store the measurements takenprior to a transmission or reception failure for each rate shift and onefor roam, as shown at steps 62 and 64. The current measurements m_(j),last data rate L_(j), and pertinent vector r_(j) are then used todetermine whether to rate shift or roam based on a function f(m_(j),L_(j), r_(j)), as shown at steps 66 and 68. The function f can be a verysimplistic function that performs a compare operation against the vectorvalues r_(j) or it can be a more sophisticated function such as takingthe median, highest, or lowest value of r_(j).

Thus, the heuristic method dynamically calculates the rate shift androam criteria based on a given wireless environment. If the wirelessenvironment changes, the decision criteria will evolve and beautomatically updated to reflect the current wireless environment. Witheach transmission or reception, the measurements are compared to therate shift and roaming criteria and the appropriate action is taken. Thevector updates and criteria updates occur after the last transmission orreception and prior to the next. In this fashion, the criteria arealways optimal. The result is a rate shift and roaming algorithm that istailored to a customer's environment and that dynamically adjusts tochanges in the wireless environment.

In accordance with a third embodiment of the present invention, a globalpositioning system (GPS) method for determining when a communicationdevice should rate shift, switch channels, or roam in a wirelessenvironment is provided. As known in the art, GPS is a system ofsatellites that provide signals for a receiver to utilize to allow it topinpoint its location on earth with precision. In referring to GPS, itmay also include differential GPS that can correct for certain errors inpositioning information at a location such as by providing additionalreference measurements taken at a known location. The GPS methoddynamically determines the criteria used to rate shift or roam byutilizing GPS information for the wireless communication device 20 andfor the access points or cells in close proximity to the position of thewireless communication device 20. As discussed further below, it ispossible to rate shift, switch channels, or roam to a different cellbased on the position of the wireless communication device 20 relativeto various cells rather than relying on signal strength or degradation.

The GPS method, illustrated in FIG. 5 in flowchart form, utilizespositioning information such as a table organized in terms of positionor vector coordinates of current and adjacent access points and theirrespective channels and status information to allow a wirelesscommunication device 20 to make an optimal access point selection. Thetable is provided by the access point (AP) to which the wirelesscommunication device 20 is initially connected, as shown at step 80.Specifically, the table will contain the following information about thewireless communication device 20, the currently connected access point,and the access points adjacent to the connected access point: 1) GPS orDifferential GPS position (G_(i)) of the wireless communication device20; 2) relative position (RP_(ij)) of the wireless communication device20 to various access points; 3) proximity threshold (PT_(ij)) for accesspoints; 4) available channel (C_(ij)) for access points; and 5) statusinformation (S_(ij)) for access points, where _(i) is a time t_(i) and_(j) is the _(j)th cell or access point. The proximity threshold(PT_(ij)) provides the maximum range of the cell or the communicationenvelope that the wireless communication device 20 must be within to bepermitted to switch to that corresponding access point. As the wirelesscommunication device transitions from one access point to another, thetable is updated. The current access point can estimate the location ofthe wireless communication device 20 or alternatively, the wirelesscommunication device 20 may obtain a GPS reading and supply thisinformation to the current access point, which can then update the tableand also apply differential GPS to refine the location measurement.

A determination is made at step 82 as to whether the relative positionRP_(ij) is less than or equal to the corresponding proximity thresholdPT_(ij) for each access point with respect to the wireless communicationdevice 20. Alternatively or in addition, through the use of a directionvector consisting of RP_(ij), RP_(i+1,j), etc., it is possible toestimate the next RP_(ij) value at some point in the future andformulate a prediction as to whether to switch the rate, channel, oraccess point, as shown at step 84. In this way, it is possible toanticipate the need to rate shift or roam prior to an unsuccessfultransmission or prior to a comparison against a fixed predefinedthreshold (PT_(ij)) and this prediction of future measurements can beperformed while the last transmission is taking place. This proactiveapproach to rate shifting and roaming may be even more critical when thewireless communication device 20 is rapidly transitioning from one cellto the next or utilizing high speed, efficient wireless communicationsthat are being introduced or will be in the near future. Whether step 82or step 84 controls may depend upon a weighting function as to whichprovides the optimal solution based upon the varying conditions. If atleast one access point meets either or both criteria of step 82 or 84,then at step 86 the wireless communication device 20 may roam to theaccess point that offers the optimal conditions such as rate, channelC_(ij), and status information S_(ij) and that is superior to thecurrent access point.

The access point S_(ij) may be utilized to assist in selecting theoptimal access point based on accessibility and congestion level,because each access point S_(ij) will have a congestion level associatedwith it that reflects its availability to accept additional traffic. Forexample, integer values could be assigned to represent the congestionlevel (e.g., 1-at capacity, 2-80% utilized, 3-60% utilized, 4-40%utilized, and 5-less than 20% utilized). Based on the status value ofthe access points S_(ij), the roaming may occur to one of the lesscongested alternative access points, assuming there is overlap of thecells at the location of the wireless communication device 20.

It should be understood that the inventive concepts described should notbe limited narrowly and that alternative embodiments may be made withinthe scope of the present invention. For example, the wirelesscommunication device 20 is determining the optimal access point based oninformation supplied by the current access point or cell. However, itshould be clear that the communication system including the current cellmay evaluate the data and determine the optimal cell for the wirelesscommunication device 20 to communicate with and further, command thewireless communication device 20 to communicate through that optimalcell. Also, although GPS is utilized to determine location and relativepositions, alternative techniques as known in the art may be utilized toprovide position and relative position information.

The placement of access points may be determined by coverage or bycapacity. In a high density area, generally capacity will determineplacement. In a low density area, desired maximum coverage willgenerally determine placement. By linking congestion level withproximity, it is possible to provide load balancing across accesspoints. An additional benefit of the GPS approach relates to 911emergency service, which currently operates by having a mobile phoneconnect to an access point and then to a specific 911 service area thatthe access point serves. Current systems do not use relative proximity,therefore it is possible for a wireless connection to be made to anaccess point that then connects to the wrong 911 service area for thelocation of the wireless communication device. This may cause confusionand critical delays in servicing a 911 call, because it delaysdispatching of the appropriate emergency service from the closestlocation or results in additional transferring among agencies until thecorrect agency for the location is contacted.

Having thus described preferred embodiments of methods for determiningwhen a communication device should rate shift or roam in a wirelessenvironment, it should be apparent to those skilled in the art thatcertain advantages of the within system have been achieved. It shouldalso be appreciated that various modifications, adaptations, andalternative embodiments thereof may be made within the scope and spiritof the present invention. For example, a wireless environment along witha wired LAN has been illustrated to show an embodiment of the presentinvention, but it should be apparent that the inventive conceptsdescribed above would be equally applicable to a wireless network orwireless communication system, as known in the art. Furthermore, thewireless communication system could comprise any type of wireless RFcommunication system and include voice and data communications as knownin the art. The invention is further defined by the following claims.

1. A method of wireless communication in a communication system, thecommunication system comprising a mobile wireless communication deviceand a plurality of transceivers, the method comprising: (a) receiving,at one of the transceivers, communication signals transmitted by themobile wireless communication device; (b) evaluating, over timeintervals, a quality of the communication signals received from themobile wireless communication device to obtain measurement values of aquality of the evaluated communication signals; (c) creating afunctional relationship value based on the measurement values and aconfigurable parameter associated with the measurement values; (d)calculating an extrapolated functional relationship value based on oneor more functional relationship values; and (e) selecting one of thetransceivers to communicate with the mobile wireless communicationdevice based on the extrapolated functional relationship value.
 2. Themethod according to claim 1, further comprising: storing the functionalrelationship value.
 3. The method according to claim 1, wherein themeasurement values comprise signal-to-noise ratios.
 4. The methodaccording to claim 1, wherein the measurement values comprise bit errorrates.
 5. The method according to claim 1, wherein the measurementvalues comprise transmission-retry counts.
 6. The method according toclaim 1, wherein the measurement values comprise at least one ofreceived signal strength indicators and energy-to-noise densities. 7.The method according to claim 1, wherein the measurement values comprisecell congestion measurement values.
 8. The method according to claim 1,wherein the plurality of transceivers comprise a plurality of accesspoints.
 9. The method according to claim 1, wherein the plurality oftransceivers comprise an access point coupled to a wired network or awireless network.
 10. The method according to claim 9, wherein theplurality of transceivers comprise an intermediary access point that (1)wirelessly communicates with the access point and the mobile wirelesscommunication device or (2) wirelessly communicates with the accesspoint and another intermediary access point.
 11. The method according toclaim 1, wherein (c) comprises determining whether to use themeasurement values, applying a weighting factor associated with themeasurement values, and applying a threshold factor associated with themeasurement values.
 12. A method of wireless communication in acommunication system, the communication system comprising a mobilewireless communication device and a plurality of transceivers, themethod comprising: (a) receiving, at one of the transceivers,communication signals transmitted by the mobile wireless communicationdevice; (b) evaluating, over time intervals, a quality of thecommunication signals received from the mobile wireless communicationdevice to obtain measurement values of a quality of the evaluatedcommunication signals; (c) detecting a failure of the communicationsignals; (d) calculating a function based on current measurement valuesand latest measurement values before the detected failure; and (e)determining whether to change transmission or reception of thecommunication signals based at least in part on the function.
 13. Themethod according to claim 12, further comprising: storing the latestmeasurement values before the detected failure.
 14. The method accordingto claim 13, wherein the detected failure comprises at least one of adetected transmission failure and a detected reception failure.
 15. Themethod according to claim 12, wherein the measurement values comprise atleast one of signal-to-noise ratios and bit error rates.
 16. The methodaccording to claim 12, wherein the measurement values comprise at leastone of numbers of transmission retries and cell congestion measurementvalues.
 17. The method according to claim 12, wherein the measurementvalues comprise received signal strength indicators.
 18. The methodaccording to claim 12, wherein the measurement values comprise bitenergy-to-noise densities.
 19. The method according to claim 12, whereinthe mobile wireless communication device and the plurality oftransceivers communicate at a variable data rate, wherein the mobilewireless communication device roams from one transceiver to anothertransceiver, and wherein (e) comprises at least one of determiningwhether the mobile wireless communication device will roam anddetermining whether the data rate will be shifted.
 20. A method ofwireless communication in a communication system, the communicationsystem comprising a roaming wireless device and a plurality of accesspoints, the method comprising: (a) receiving, at one of the accesspoints, communication signals transmitted by the roaming wirelessdevice; (b) evaluating, over time intervals, a quality of thecommunication signals received from the roaming wireless device toobtain measurement values of a quality of the evaluated communicationsignals; (c) creating a functional relationship value based on themeasurement values and a configurable parameter associated with themeasurement values; (d) storing the functional relationship value; (e)calculating an extrapolated functional relationship value based on astored functional relationship value; and (f) selecting one of theaccess points to communicate with the roaming wireless device based onthe extrapolated functional relationship value.